Hi,
I had a quick look at the E3631 schematic. The ADC circuitry is much better than the DAC and the rest of the power supply from a precision point of view. For example the TL074 op-amps used in the output voltage control have a typical offset drift specification of 18uV/C. This is gained up by the circuit, around 12, to 216uV/C.
Also the DAC is shared, using a mux and track and hold circuits between 8 outputs. (Tektronix did this in the TDS5xx and TDS7xx scopes. It is one of the things that goes bad if the electrolytics leak on the board)
The ADC is much better. It is
*possible*, I don't know, it depends on the firmware, that the DAC is being disciplined by the ADC, so that it doesn't need to be that good, just have lots of resolution.
Regards,
Jay_Diddy_B